Various devices such as bar code scanners, compact disk players, DVD players, range finders, designators, etc. use light to perform various functions, such as read data from optical media. Beams of light are also used in devices in communication devices, sample analyzing devices, pointing and designating devices, distance measurement devices, and time measurement devices.
Light can be controlled using standard lenses and mirrors. These passive methods can be made active via mechanical motion. For example, mirrors can be placed on galvo-motors to move the mirror to control the direction of light propagation. This technique is used in barcode scanners, or optical read/write heads in CD/DVD players. However, mechanical control over light is undesirable for several reasons. First, it is difficult to make such mechanical devices compact. Second, the mechanical nature of such moving devices have limited lifetimes due to mechanical wear and failure issues. Third, mechanical devices are inherently vibration sensitive, which limits the type of environment in which they can be used. Finally, mechanical devices necessitate a level of design complexity including gears, bearings, and other mechanical components, which add cost, expense, and maintenance issues to such designs.
Rather than move a lens or a mirror with a motor or actuator, light can be controlled through the use of waveguides. For instance, U.S. Pat. No. 5,347,377 entitled “Planar Waveguide Liquid Crystal Variable Retarder” relates generally to providing an improved waveguide liquid crystal optical device, and discloses in Table 1 the use of alternating current voltages between 2 and 50 volts rms. This patent teaches controlling only the optical phase delay for only TM polarized light.
With conventional waveguides, electro-optic materials are employed whereby a voltage applied across the material changes the index of refraction, n. However, with conventional techniques, the index of refraction can only be changed a very small amount, such as 0.0001 per kilovolt for bulk materials. This limitation makes this type of light control extremely limited, and to date not a viable alternative to mechanical control of light.
While liquid crystal optics have become widespread in display applications, in such applications light is attenuated but not steered nor refocused, or only to a very small degree. In order to use conventional techniques for liquid crystal optics to achieve active optical control, prohibitively thick layers of liquid crystal (>100 microns) would be needed, which would render the device highly opaque and slow. The thick layers of liquid crystal can take seconds or even minutes to change, and are difficult or impossible to control. Although electro-optic beam-steerers have been made with standard thin liquid crystal cells, such devices have only realized minimal control (in the range of micro-degrees of steering).
U.S. Pat. No. 3,963,310 to Giallorenzi et al. entitled “Liquid Crystal Waveguide” teaches of utilizing liquid crystal-within the core of a waveguide. However, as recognized by the present inventors, such a waveguide would be problematic in that there would be substantial losses or attenuation of light traveling through such a waveguide. Furthermore, such a waveguide does not provide for control of light in a direction out-of-the-plane of the waveguide.
Accordingly, as recognized by the present inventors, what is needed is a liquid crystal waveguide for controlling light that permits active control of the propagation of light through and out of the waveguide.